Transitioning cat from kitten food to adult cat food?



My kitten turns one the first week of August, and I figured I need to start feeding him adult cat food. (He is eating Purina Kitten Chow now, and I plan on feeding him an indoor Purina Cat Chow Complete Formula.)I was wondering how I should go about transitioning him to the adult food. Do I just completely switch the food one day or do it gradually so it wont upset his stomach?